Pyridoxine (vitamin B.sub.6) is a well known vitamin normally used as an adjunct in prophylaxis and treatment of multiple vitamin B complex deficiencies. It is also used in dermatoses, neuromuscular and neurological diseases.
An important synthetic procedure for pyridoxine involves the use of 4-methyl-5-cyanooxazole as a key intermediate. A typical synthetic procedure is that of Kimel et al., disclosed in U.S. Pat. No. 3,250,778, wherein 4-methyl-5-cyanooxazole is condensed with a 4,7-dihydro-1,3-dioxepin followed by acid hydrolysis of the resultant product to form pyridoxine. However, there is a continuing search to find more efficient and economical methods of producing the 4-methyl-5-cyanooxazole intermediate. Prior methods of preparing this intermediate have involved either heating 4-methyloxazole-5-carboxamides with phosphorous pentoxide or utilizing conventional amide dehydrating agents, such as phosphorous oxyhalides, to form the corresponding nitriles. These procedures were fraught with disadvantages such as charring, poor yields, equipment corrosion and unwanted by-products. One solution to the above problems is disclosed in a patent to Chase, U.S. Pat. No. 3,222,374, wherein the 4-lower alkyl-5-carboxamide is reacted with phosphorus pentoxide in the presence of a solvent such as quinoline. The following reaction scheme is illustrative of the preparation of 4-lower alkyl-5-cyanooxazole employing the Chase improvement: ##STR1## wherein R.sub.1 and R.sub.2 are lower alkyl.
A disadvantage of the above procedure is that the conversion of the amide group to a nitrile is very expensive, thus resulting in a loss of economy and efficiency. An additional disadvantage is that disposal of spent P.sub.2 O.sub.5 and quinoline pose a serious pollution problem.
The instant invention provides to the art a method for the preparation of 4-lower alkyl-5-cyanooxazoles which is efficient, economical and free of the disadvantages of the procedures known heretofore.